PO420 code
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Junior Member
Joined: Nov 2012
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PO420 code
Hello,
I have an '07 with a 5.4 with 100K. For a while I have been experiencing a misfire at around 45-50 mph (under load). My mechanic said it was most likely a bad coil and eventually I would get a code telling which cylinder. After living with the misfire for a while it finally gave me a PO420 code indicating a bat CAT. I believe the CATs are damaged from the misfire but still no indication as to what cylinder may have a bad coil.
The misfire has gotten worse and I am sick of driving it this way. The truck had a tuneup at 70K. I don't want to start throwing money at this, such as changing all 8 coils, without really knowing what the problem is.
Could the original misfire have been caused by a bad CAT? Mechanic's recommendation is to wait for a code on the coil.
Thanks for any advice.
I have an '07 with a 5.4 with 100K. For a while I have been experiencing a misfire at around 45-50 mph (under load). My mechanic said it was most likely a bad coil and eventually I would get a code telling which cylinder. After living with the misfire for a while it finally gave me a PO420 code indicating a bat CAT. I believe the CATs are damaged from the misfire but still no indication as to what cylinder may have a bad coil.
The misfire has gotten worse and I am sick of driving it this way. The truck had a tuneup at 70K. I don't want to start throwing money at this, such as changing all 8 coils, without really knowing what the problem is.
Could the original misfire have been caused by a bad CAT? Mechanic's recommendation is to wait for a code on the coil.
Thanks for any advice.
Senior Member
Joined: Dec 2006
Posts: 43,532
Likes: 817
From: Joplin MO
Change them all. Buy a 10 pack so you have a couple spares.
http://www.ebay.com/itm/NEW-IGNITION...759de9&vxp=mtr
You will pay almost that much for ONE at a parts store and those cheap Chinese coils generally work okay. You should have done something before damaging the cat - those aren't cheap and you are out of warranty.
http://www.ebay.com/itm/NEW-IGNITION...759de9&vxp=mtr
You will pay almost that much for ONE at a parts store and those cheap Chinese coils generally work okay. You should have done something before damaging the cat - those aren't cheap and you are out of warranty.
Senior Member
Joined: Oct 2002
Posts: 7,295
Likes: 125
From: St. Louis (Out in the woods)
The (now) bad cat was caused by the misfire. Fix the misfire, and, if you get lucky, then the cat *might* clear up. Don plan on it, but you might get lucky.
Finding a mild misfire before it codes isn't rocket science. All you need is to poke into the MISFIRECNT PIDs with a scan tool in Mode 6 to see which cylinder(s) is the problem.
Finding a mild misfire before it codes isn't rocket science. All you need is to poke into the MISFIRECNT PIDs with a scan tool in Mode 6 to see which cylinder(s) is the problem.
